Adenomyosis is characterised on MRI by junctional zone (JZ) thickening. Which JZ thickness threshold on T2-weighted MRI is the current diagnostic criterion for adenomyosis, and why is this zone relevant pathologically?

• A JZ ≥ 12 mm; the junctional zone represents the outer myometrium and is the site of serosal endometriosis
• B JZ ≥ 5 mm; the junctional zone is the intermediate trophoblast invasion layer
• C JZ ≥ 8 mm; the junctional zone represents the inner one-third of the myometrium and is the subendometrial myometrium where basalis glands invade ✓
• D JZ ≥ 15 mm; the junctional zone represents the decidual layer of the endometrium

Explanation

The junctional zone (JZ) is the innermost layer of the myometrium (subendometrial myometrium) and appears as a hypointense band on T2-weighted MRI. It is pathologically distinct from the outer myometrium in its cellular density, peristaltic function, and hormone sensitivity. A JZ thickness ≥ 8 mm on MRI is the accepted diagnostic threshold for adenomyosis per the MUSA (Morphological Uterus Sonographic Assessment) group and European Society of Gynaecological Endoscopy (2022), though some studies use ≥ 12 mm for greater specificity. In adenomyosis, endometrial glands and stroma from the basalis layer invade into and through the JZ, causing JZ thickening and the T2-bright foci (ectopic glands) within the hypointense JZ.

Reference: Shaw's Textbook of Gynaecology, 17th ed.

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Written and medically reviewed by the StethoPrep medical team.